In the manufacture and packaging of ground coffee, the roasted coffee beans are ground into the well-known granular form and then dispensed into individual coffee cans at a weighing and filling station placed along a coffee production line. Empty coffee cans are transported past the station where predetermined amounts by weight of coffee, typically one pound, are delivered into open cans. During such filling, the cans are vibrated to settle the coffee and thus, more densely package the ground coffee in the can.
Since the shelf life of coffee deteriorates in the presence of oxygen, the filled coffee cans are passed into a vacuum chamber where air is removed and a lid applied over the opening to thus vacuum-pack the ground coffee. In such coffee packing, it is desired to keep the free head space in each can as small as possible while still being able to accommodate a pound of coffee in a standard one pound can with different ground coffee densities.
Coffee density variations arise by virtue of the nature of the coffee beans themselves, the grinding process, and the handling of the ground coffee during the packing process. Some control over coffee density can be exercised during grinding, but such control is not always sufficient to assure that a pound of coffee will fit into a standard one pound can.
Coffee cans can be made larger to accommodate low density coffee, but then the cans designated for a particular weight will vary in size and the cans become more expensive. As a practical matter, therefore, low coffee densities are difficult to accommodate.
Initially after ground coffee has been vacuum-packed, the vacuum inside the can results in large atmospheric forces on the can wall. After some time, however, gases are released from the ground coffee and provide sufficient internal pressurization to counterbalance atmospheric pressure. One could, therefore, use a smooth-walled can and hold it in a vacuum until these internal gases build up. This, however, is not practical with typical ground coffee packaging lines where thousands of cans are processed in short time intervals.
Conventional coffee cans, therefore, are provided with regularly-spaced horizontal annular beads. These beads serve to strengthen the can wall and avoid its partial collapse, known as paneling, arising right after vacuum packing. Paneling problems become particularly frequent when the can wall is made very thin or when the can beads are eliminated. Elimination of beads is desirable to improve can appearance and enable use of other can materials such as plastic.
Techniques have been described to utilize the ground coffee to provide sidewall support in a vacuum packing process. For example, in U.S. Pat. Nos. 3,056,244 and 3,517,475, an uncontrolled pile of ground coffee is formed in the can and is then compressed after the coffee can has been vacuum packed by shortening or collapsing the can body. The compression provides a counterbalancing force against paneling of the coffee can. In U.S. Pat. No. 3,117,873, the ground coffee is compressed by bowing-in the can lid, thus reducing the volume of the can.
These coffee compressions techniques do not handle density variations and may, therefore, not function satisfactorily. Problems are encountered when the ground coffee is excessively compressed so as to form in essence a rigidity that resists easy dispensing when the coffee can is opened by a consumer.